The present invention relates to a protective film for a polarizing plate, which exhibits excellent adhesive properties, and a polarizing plate employing the same, and a production method thereof, and further to a production method of cellulose ester film which exhibits excellent recycling properties.
As a protective film employed in the polarizing plate of a liquid crystal display, cellulose esters such as triacetyl cellulose and the like, are suitable due to their lower double refraction, and have frequently been employed.
Commonly, a polarizing plate has such a structure that a polarizing film comprised of a polyvinyl alcohol film and the like, in which iodine or dyes are absorbed and oriented, is laminated on both sides with transparent resin layers. Frequently employed as said transparent resin layer is a protective film comprised of triacetyl cellulose film.
When a polarizing plate is produced by adhering a protective film with a polarizer, in order to readily apply a water-soluble adhesive, a protective film such as triacetyl cellulose film, and the like is temporarily subjected to saponifying treatment through immersion in an alkali solution having a high concentration at a relatively high temperature so that the film surface becomes hydrophilic. Then, an adhesive is applied to said protective film which is adhered with the polarizer. However, it is preferred to make a transparent resin film hydrophilic without employing chemicals for saponification, which are not preferred in view of work as well as troublesome processes.
Further, for a transparent resin film employed as the protective film for the polarizer, triacetyl cellulose is exclusively employed. One of the reasons why triacetyl cellulose has not been replaced by other films is that the other films are not subjected to saponification. Accordingly, another process, which replaces saponification, has been sought.
The present inventors have investigated various methods to make the surface of a transparent resin film hydrophilic, which replace saponification. As a result, it has been discovered that when a transparent resin film is subjected to plasma treatment, it exhibits similar performance obtained by saponification.
An object of the present invention is to provide a highly efficient protective film for the polarizing plate, which is readily adhered with polyvinyl alcohol film employed as a polarizer, can be produced employing processes which are safe in view of operation and do not adversely affect the environment, and exhibits excellent adhesion with a polyvinyl alcohol film layer, and a polarizing plate employing the same.
Further, another object is to obtain a protective film for the polarizing plate, in which moisture resistance is enhanced employing safe methods for operation, and which exhibits excellent durability. Further, it is possible to obtain a protective film for the polarizing plate, which comprises cellulose ester film which is readily recycled. Still further, it is possible to obtain a polarizing plate as well as a liquid crystal display unit which exhibit excellent durability.
An outline of the present invention will now be described.
1. A protective film for a polarizing plate comprising: a base material, the protective film for the polarizing plate wherein in analysis of bonding state of a carbon atom (C1s)employing X-ray photoelectron spectroscopy, when a peak having the lowest bonding energy is designated as a first peak, a peak positioned at 1.60xc2x10.3 eV on the higher bonding energy side from the first peak is designated as a second peak, and a peak positioned at 4.10xc2x10.3 eV on the higher bonding energy side from the first peak is designated as a third peak, bonding state of carbon atom C1s on a surface of at least one side of the base material and bonding state of internal carbon atom C1s in an optional depth of 0.05 to 1 xcexcm from the surface satisfy relationship described below:
Sxe2x88x92Ixe2x89xa70.1
wherein S is intensity of the second peak on the base material surface of the protective film for the polarizing plate/intensity of the first peak on the base material surface of the protective film for the polarizing plate, and I is intensity of the second peak in the interior of the base material of the protective film for the polarizing plate/intensity of the first peak of the interior of the base material of the protective film for the polarizing plate.
2. A protective film for the polarizing plate described in claim 1, wherein Sxe2x89xa71.60.
3. The protective film for the polarizing plate described in claim 1, wherein the bonding state of carbon atom C1s on the surface of the protective film for the polarizing plate satisfies relationship described below:
Txe2x89xa70.2
wherein T is intensity of the third peak on the base material surface of the protective film for the polarizing plate/the intensity of the second peak on the base material surface of the protective film for the polarizing plate.
4. The protective film for the polarizing plate described in claim 1 wherein the contact angle of the surface of the base material with respect to pure water is less than 55 degrees.
5. The protective film for the polarizing plate described in claim 1 wherein the contact angle of at least one surface of the protective film for the polarizing plate with respect to pure water is less than 55 degrees.
6. The protective film for the polarizing plate described in claim 1 wherein the surface of the base material is subjected to plasma treatment.
7. The protective film for the polarizing plate described in claim 1, comprising a hydrophilic layer containing a hydrophilic high molecular compound.
8. The protective film for the polarizing plate described in claim 1, wherein the base material is cellulose ester film, polycarbonate film, polyester film, or polyacryl film.
9. The protective film for the polarizing plate described in claim 1, wherein the average of the central line average roughness Ra of 10 points on the surface of the protective film for the polarizing plate is between 1 and 80 nm, and the average of the maximum height differences of 10 points arbitrary of said surface is between 5 and 80 nm.
10. A protective film for the polarizing plate, comprising a base material and an auxiliary layer, a protective film for the polarizing plate wherein in analysis of bonding state of carbon atom (C1s) employing X-ray photoelectron spectroscopy, when a peak having the lowest bonding energy is designated as a first peak, a peak positioned at 1.60xc2x10.3 eV on the higher bonding energy side from the first peak is designated as a second peak, and a peak positioned at 4.10xc2x10.3 eV on the higher bonding energy side from the first peak is designated as a third peak, bonding state of carbon atom C1s on a surface of at least one side of the auxiliary layer and bonding state of internal carbon atom C1s of the auxiliary layer in an optional depth of 0.05 to 1 xcexcm from the surface satisfy relationship described below:
Sxe2x80x2xe2x88x92Ixe2x80x2xe2x89xa70.1
wherein Sxe2x80x2 is intensity of the second peak on the auxiliary layer surface of the protective film for the polarizing plate/intensity of the first peak on the auxiliary layer surface of the protective film for the polarizing plate, and Ixe2x80x2 is intensity of the second peak in the interior of the auxiliary layer of the protective film for the polarizing plate/intensity of the first peak of the interior of the auxiliary layer of the protective film for the polarizing plate.
11. A protective film for a polarizing plate, comprising a base material wherein at least one surface of the base material is subjected to plasma treatment.
12. A protective film for a polarizing plate, comprising a base material and an auxiliary layer, wherein the surface of the auxiliary layer is subjected to plasma treatment.
13. A polarizing plate, comprising a first protective film, polarizer and a second protective film, wherein at least one of the first protective film and the second protective film comprises a base material, and in analysis of bonding state of a carbon atom employing X-ray photoelectron spectroscopy, when a peak having the lowest bonding energy is designated as a first peak, a peak positioned at 1.60xc2x10.3 eV on the higher bonding energy side from the first peak is designated as a second peak, and a peak positioned at 4.10xc2x10.3 eV on the higher bonding energy side from the first peak is designated as a third peak, bonding state of carbon atom C1s on the surface of at least one side of the base material and bonding state of internal carbon atom C1s in an optional depth of 0.05 to 1 xcexcm from the surface satisfy relationship described below:
Sxe2x88x92Ixe2x89xa70.1
wherein S is intensity of the second peak on the base material surface intensity of the first peak on the base material surface, and I is intensity of the second peak in the interior of the base material intensity of the first peak of the interior of the base.
14. A liquid crystal display unit comprising a first polarizing plate, a liquid crystal cell, and a second polarizing plate provided in the inside of the first polarizing plate and the liquid crystal cell, wherein the first polarizing plate comprises
a first polarizer,
a first protective film provided to the surface of the first polarizer on the side which does not face the liquid crystal cell, and
a second protective film provided on the surface of the first polarizer on the side which faces the liquid crystal cell;
the second polarizing plate comprises
a second polarizer,
a third protective film provided to the surface of the second polarizer on the side which faces the liquid crystal cell, and
a fourth protective film provided to the surface of the second polarizer on the side which does not face the liquid crystal cell;
at least one of the first protective film, the second protective film, the third protective film, and the fourth protective film comprises a base material; and in analysis of bonding state of a carbon atom (C1s) employing X-ray photoelectron spectroscopy, when a peak having the lowest bonding energy is designated as a first peak, a peak positioned at 1.60xc2x10.3 eV on the higher bonding energy side from the first peak is designated as a second peak, and a peak positioned at 4.10xc2x10.3 eV on the higher bonding energy side from the first peak is designated as a third peak, bonding state of carbon atom C1s on a surface of at least one side of the base material and bonding state of internal carbon atom C1s in an optional depth of 0.05 to 1 xcexcm from the surface satisfy relationship described below:
Sxe2x88x92Ixe2x89xa70.1
wherein S is intensity of the second peak on the base material surface intensity of the first peak on the base material surface, and I is the intensity of the second peak in the interior of the base material intensity of the first peak of the interior of the base.
15. A production method of a protective film for a polarizing plate, comprising the following steps, and a step in which a prepared film is subjected to plasma treatment.
16. The production method described in claim 15, wherein the plasma treatment is a vacuum glow discharge, an atmospheric pressure glow discharge, or a flame plasma treatment.
17. The production method described in claim 15 wherein the plasma treatment is carried out a plurality of times.
18. The production method described in claim 15, wherein the plasma treatment is subsequently or simultaneously carried out under the conditions in which the Cxe2x80x94C bond or Cxe2x80x94H bond of the organic substance on the film surface is broken, or a hydroxyl group or amino group is formed on the film surface.
19. A production method of a polarizing plate comprising following steps:
a step in which the surface of a polarizer or a surface of a protective film for the polarizing plate is subjected to plasma treatment, and
a step in which the protective film subjected to plasma treatment for the polarizing plate is adhered with at least one of polarizer surfaces or a protective film for the polarizing plate is at least one of polarizer surfaces subjected to plasma treatment.
20. The production method described in claim 19, wherein after plasma treatment and before adhering the protective film for the polarizing plate with a polarizer, the surface which has been subjected to plasma treatment is washed with water.